Im In Trouble
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Elder User
Joined: Aug 2006
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From: foristell, missouri
Im In Trouble
i cant pass my inspection on my 1990 f250 351 5-speed cause my high beams don't work(how dumb). when i hit the foot-switch the headlights go completely out instead of turning the highs on. WHAT COULD IT BE. i don't do well with electrical stuff, i usually end up throwing and breaking things so i thought i would get some advice first this time. cause i cant afford to mess anything up since i also have to put catalytic converters on it. also does anybody know where to get cheap cats cause Im gonna knock the innards out anyways.
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From: Baltimore
Each headlight bulb has 2 filaments. One for high beam and one for low beam.
When you press on the floor mounted dimmer to turn on the high beams does the high beam indicator on the dash turn on?
If it does that tells you the switch is good and could be both high beam filaments are burnt out. You can remove the bulb from the backside of the headlight housing.
The bulbs are haolgen. Don't touch the glass part of the bulb with your bare hand because you can leave grease from your hand on it which can cause the bulb to fail.
You can remove the bulb and use a ohm meter to see if the filament is good.
Here's the diagram for a 88. Your 90 should be the same.
When you press on the floor mounted dimmer to turn on the high beams does the high beam indicator on the dash turn on?
If it does that tells you the switch is good and could be both high beam filaments are burnt out. You can remove the bulb from the backside of the headlight housing.
The bulbs are haolgen. Don't touch the glass part of the bulb with your bare hand because you can leave grease from your hand on it which can cause the bulb to fail.
You can remove the bulb and use a ohm meter to see if the filament is good.
Here's the diagram for a 88. Your 90 should be the same.
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Joined: Oct 2005
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From: Berlin, CT USA
You know i had the same problem in my 87 f150 floor switch, since i had some runst made air vents in the cab moisture and when it rained thing slowely started to crap out, so i ripped it out put in a new one in the dash lol 2 weeks later truck went to the junk yard HA
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Joined: Dec 2006
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From: Hillsboro, OR
If the indicator on the dash does not light up when you step on the switch, then either the switch is bad or the connections are ugly. Unplug the connector and jump the wires to the high beams. See if that works.
Since I am bad with electrics as well, here is how I would do it:
Unplug the connection.
Draw the plug for reference later.
Use a test light to find power when the lights are on. Mark this on your cartoon.
Reverse the test light so that it has power and find the ground in the plug. Mark this in the drawing
The other two(?) sockets should be for low and high. Jump those and see if you have lights.
Hope this helps.
Since I am bad with electrics as well, here is how I would do it:
Unplug the connection.
Draw the plug for reference later.
Use a test light to find power when the lights are on. Mark this on your cartoon.
Reverse the test light so that it has power and find the ground in the plug. Mark this in the drawing
The other two(?) sockets should be for low and high. Jump those and see if you have lights.
Hope this helps.
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Elder User
Joined: Aug 2006
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From: foristell, missouri
thanks guys i just tried workin on it and almost put my fist through the firewall. i hate electrical crap i just dont understand it. i think the switch or the bulbs are bad case the light in the dash dont come on.
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Elder User
Joined: Aug 2006
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From: foristell, missouri
when the switch is on for the highbeams both wires have power but the lights are only on low, and when the switch is on the dimmer part for lowbeams the lights go out completely. i alredy busted one of the bulbs so ill have to go get at least one new one tomorrow so i guess ill just get 2 in case.
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Elder User
Joined: Dec 2006
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From: Hillsboro, OR
Looking at F150's cartoon, it looks like it is just one power in and two out depending on what you want (my bad for not looking at it closer on my first post). What happens when you jump these? It looks like a three prong switch with the main power coming in to the center plug. Run an insulated wire from the center plug to one of the side plugs and see if the lights come on. Then try the other one. This should get you closer to the problem.
As a side note. I used to get quite frustrated when working on my vehichles in my younger days. One day, I got so pissed at the '67 Dodge van and the 'ol lady, I smacked the 3-on-the-tree while it was running. With the 225 slant six, it ground into gear and took off. I nearly killed my girlfrend and ran the van into my neighbor's house (I was in the back at the time and could not get it back out of gear).
The point is: I know these things can be frustrating but when you destroy a part or your hand punching the truck, all you are doing is giving your money to the parts house or the hospital.
I set up a punching bag in my garage and used it quite often. Hope this helps.
As a side note. I used to get quite frustrated when working on my vehichles in my younger days. One day, I got so pissed at the '67 Dodge van and the 'ol lady, I smacked the 3-on-the-tree while it was running. With the 225 slant six, it ground into gear and took off. I nearly killed my girlfrend and ran the van into my neighbor's house (I was in the back at the time and could not get it back out of gear).
The point is: I know these things can be frustrating but when you destroy a part or your hand punching the truck, all you are doing is giving your money to the parts house or the hospital.
I set up a punching bag in my garage and used it quite often. Hope this helps.
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Elder User
Joined: Aug 2006
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From: foristell, missouri
i think i can figure it out it just makes me mad that i have to have high beams for inspection, i have honestly never turned them on, thats why i didnt know they were out. for some reason the last inspector didnt catch the lights or the cats. i do apreciate the the help cause like i said dont do electrical but put a blown motor in my hands and ill be fine for a week. any thing where i can see the new part and the old one it needs to replace and i have no problems at all.
the last time i worked on electrical crap was on my 91 i had and i ended up with a broken wrist and a dented bed, not fun cause then i had to do body work, also something i hate.
the last time i worked on electrical crap was on my 91 i had and i ended up with a broken wrist and a dented bed, not fun cause then i had to do body work, also something i hate.
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Joined: Jan 2002
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From: Baltimore
If the high beam indicator doesn't come on when in high beam mode, the floor switch is bad. If you buy another one, for test purposes if you can, just plug it in before removing the old one.
Here's how the circuit works.
Assuming the color of the wires are the same as your 90.
From the Headlight switch when the low beams are on, 12 volts comes from the Red wire with a yellow strip, goes thru the Dimmer switch to the red with black strip wire to the low beam filament of both headlight bulbs then to ground.
From the Headlight switch when in high beams are on, 12 volts comes from the Red wire with a yellow strip, goes thru the Dimmer switch to the Light green wire with a black stripe to the high beam filaments of both headlight bulbs then to ground.
12 volts also goes to the 2nd Light green wire with a black stripe to the instrument cluster high beam bulb which should light up.
Your symtom points to a bad dimmer switch.
When you switch the dimmer switch from low beam to high beam the low beam filament should go out. That's normal.
Here's how the circuit works.
Assuming the color of the wires are the same as your 90.
From the Headlight switch when the low beams are on, 12 volts comes from the Red wire with a yellow strip, goes thru the Dimmer switch to the red with black strip wire to the low beam filament of both headlight bulbs then to ground.
From the Headlight switch when in high beams are on, 12 volts comes from the Red wire with a yellow strip, goes thru the Dimmer switch to the Light green wire with a black stripe to the high beam filaments of both headlight bulbs then to ground.
12 volts also goes to the 2nd Light green wire with a black stripe to the instrument cluster high beam bulb which should light up.
Your symtom points to a bad dimmer switch.
When you switch the dimmer switch from low beam to high beam the low beam filament should go out. That's normal.
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Elder User
Joined: Aug 2006
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From: foristell, missouri
i finally figured it out, there was a separate aftermarket switch under the dash that i guess ran some off road lights, but..... it took power from the headlights and when it did that the person who hooked it up messed up the high-beam connections so they never got power. what an idiot, if your gonna modify something do it right or dont do it at all. thanks for all the tips guys they all helped in narrowing it down to some sort of switch.